1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2003-282860 has disclosed a method for forming a gate insulating film on the face of a silicon substrate, forming a gate electrode on the gate insulating film, removing the exposed gate insulating film by wet etching, and forming an oxide film on the gate electrode and the exposed portion of the silicon substrate by thermal oxidation. In this method, undercuts are formed in lower portions of the side faces of the gate electrode by wet etching. These undercuts are reduced by thermal oxidation following wet etching, and filled with the silicon oxide film formed by low-pressure CVD following thermal oxidation.
When the undercuts as described above are formed, variations are readily produced in the structure of the end portion of the gate insulating film, and this can vary the characteristics (for example, the threshold value and current driving capability) of a MOS transistor.